The gum elastic bougie was first described by Macintosh in 1949  and is an extremely useful intubation aid in many circumstances. It was used successfully in 66% of 2000 reports of difficult intubation . It may be used on its own or via a laryngeal mask airway [3,4]. In such circumstances, the gum elastic bougie is often blindly placed into the trachea. Correct placement is suggested if the tip of the gum elastic bougie is felt to run over the tracheal rings or resistance is felt when the tip reaches the small airways. Neither clicks or hold up are usually encountered with oesophageal placement of the gum elastic bougie . This is not 100% accurate and confirmation by auscultation and capnography must await placement of the endotracheal tube. If the gum elastic bougie has not been correctly positioned, then there will be a delay until it is repositioned and tracheal intubation performed. In the emergency situation this delay is undesirable. This study evaluates a gum elastic bougie that has been modified to enable capnography to confirm correct placement. Delay in tracheal intubation will also delay oxygenation. Insufflation of oxygen through the gum elastic bougie may delay the onset of severe oxygen desaturation. The second part of this study evaluates the gum elastic bougie for this use.
The Eschmann gum elastic bougie (SIMS Portex, Hythe, Kent, UK) is hollow except at its two ends, so two holes were drilled (by one author, FAM) – one at each end. The capnograph sampling tubing was attached to the proximal end of the gum elastic bougie by a 16 G intravenous (i.v.) cannula. Following ethics committee approval, 40 patients were studied, aged 18–60 years, ASA I or II, who were scheduled for elective surgery. Patients with a predicted difficult intubation or who required a rapid sequence induction were excluded. Informed consent was obtained. All patients received general anaesthesia with preoxygenation, i.v. induction, a nondepolarizing muscle relaxant and endotracheal intubation. Patients were randomly allocated to one of two groups using the sealed envelope method. After the onset of muscle relaxation, but prior to tracheal intubation, each patient had the gum elastic bougie inserted according to the randomization. Patients in Group 1 had the gum elastic bougie placed in the trachea, whereas it was placed in the oesophagus in patients in Group 2. A blinded observer (consultant anaesthetist) was asked to study the capnograph waveform, record the end-tidal CO2 values at 10 and 20 s, and deduce where the gum elastic bougie was placed. The same observer was used for all patients. The patient's trachea was then intubated and anaesthesia continued as required for the procedure. The gum elastic bougie was cleaned with Hibiscrub®, rinsed and allowed to dry between patients.
To assess the adequacy of the gum elastic bougie for apnoeic oxygenation, we used the METI (Medical Education Technologies Incorporated, Sarasota, Florida, USA) anaesthetic simulator. The model used was a standard adult male with a calculated shunt fraction of 0.02. We performed a total of 17 experiments, seven with apnoeic oxygenation and 10 without (controls). Each experiment started with the simulator programmed to breath air spontaneously for 5 min. Then preoxygenation for three minutes with a face mask, circle system and oxygen flowing at 8 L min−1 was instituted. Anaesthesia was induced with propofol 200 mg via the drug entry system and 100% neuromuscular blockade programmed. In the seven apnoeic oxygenation experiments, we inserted the gum elastic bougie (the tip positioned 2–3 cm beyond the vocal cords), after neuromuscular blockade, with 8 L min−1 of oxygen flowing through it. The 10 controls had no gum elastic bougie inserted, neither were given oxygen. We measured the time taken for the oxygen saturation to fall to 90%.
Three patients were excluded for technical problems (kinking of the capnograph connection at the cannula) leaving a total of 37 patients: 18 in the tracheal group and 19 in the oesophageal group. The position of the gum elastic bougie was correctly predicted by the blinded observer in 89.2% of patients. The CO2 readings (Table 1) obtained from the trachea and the oesophagus at 10 and 20 s were significantly different (P < 0.001 Wilcoxon signed rank). At 10 s, the medians (range) of the tracheal and oesophageal groups were 3.49 kPa (0–6.32 kPa) and 0.13 kPa (0–4.21 kPa), respectively. At 20 s, the medians (range) of the tracheal and oesophageal groups were 3.75 kPa (0.13–5.53 kPa) and 0.13 kPa (0–1.32 kPa), respectively. If a PCO2 > 0.66 kPa was assumed to be predictive of tracheal placement, then PCO2 readings at 10 s gave a sensitivity of 0.88 and a specificity of 0.684. At 20 s, the sensitivity was 0.89, a specificity of 0.95, a positive predictive value of 0.94 and a negative predictive value of 0.9. If 20 s is deemed too long to wait, then a PCO2 value greater than 1.33 kPa at 10 s gives the best results – sensitivity of 0.78, specificity of 0.84, a positive predictive value of 0.77 and a negative predictive value of 0.8.
The presence of a pulsatile CO2 waveform was occasionally noted. This occurred in four patients and was associated with a gum elastic bougie placed in the trachea.
In the apnoeic oxygenation group, the average time to SpO2 of 90% was 14 min 14 s (range 11 min 10 s – 16 min 26 s). In the nonoxygenation group, this time was significantly less, average 5 min 6 s (range 4 min 44 s – 5 min 36 s), P < 0.001.
The modifications described allow the gum elastic bougie to be used in conjunction with another useful intubation aid – the capnograph. Using the capnograph did not improve the technique of ‘clicks and holdup’ as described by Kidd and his colleagues , 89.2% vs. 89.7%. However, it is a more objective method for correct placement of the gum elastic bougie, but it is slower and this may be of importance in an emergency situation. There is a 10% risk of gastric insufflation if this bougie is used for apnoeic oxygenation, thus caution should be exercised if it is to be used in this manner. However, if direct visualization confirms correct placement, its use as an apnoeic oxygenator may be useful should there be difficulties passing the endotracheal tube.
The gum elastic bougie has been used in conjunction with the laryngeal mask airway to aid tracheal intubation [3,4]. The use of capnography may help guide the hollow gum elastic bougie into the trachea, especially in spontaneously breathing patients.
The technique of apnoeic oxygenation is not new, but using it with the gum elastic bougie may be of use in the difficult intubation situation usually associated with oxygenation difficulties. The extra minutes gained using this technique could prove vital. In this study, we did not vary the physiological model which is a potential flaw. Nevertheless, it does show the potential for such simulators in the bench testing of anaesthetic apparatus and the training of anaesthetists in their proper use, with the added benefit of no patient harm. This we believe is the first use of an anaesthetic simulator to assess anaesthetic equipment.
We have described a modification to the gum elastic bougie that allows for a more objective assessment of correct placement than the previous tactile methods described and its use for apnoeic oxygenation. The current design of gum elastic bougie is unsuitable for frequent use in this setting – the interior wall is rough and therefore difficult to clean adequately. However, it should not be impossible to overcome this problem and to design a more suitable capnography connection, thereby adding another tool to the armamentarium of the anaesthetist faced with a difficult tracheal intubation.
Mr Ian Ballard, Head Technician, Scottish Anaesthesia Simulator Centre, Stirling, Scotland, UK.
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